This invention relates to methods and apparatus for continuous and/or intermittent monitoring of central venous and pulmonary artery pressures. More particularly, it relates to methods and apparatus for selectively interconnecting the pressure monitoring output ports of a multi-lumen catheter to a single pressure monitoring apparatus, such as a transducer or the like, so that a single pressure monitoring apparatus may be used to selectively monitor pressures in a plurality of locations by simple switching of selector valves.
Various therapeutic and diagnostic tools have recently been developed to assist in monitoring of body functions and conditions and in treatment of critically ill patients. Although many of such tools may appear to be of simple design, their use often requires complex and expensive electronic apparatus to interpret and record the functions monitored and further requires highly trained staff personnel for proper safe and effective use. Typical of such diagnostic tools is the Swan-Ganz catheter. This apparatus comprises a multi-lumen catheter designed and adapted for insertion into the right ventricle through the right atrium and, when properly used, can monitor blood temperature, pulmonary artery pressure and even pulmonary capillary wedge pressure. In various modifications, the apparatus can be used for direct solution injection to determine cardiac output by thermodilution and may incorporate electrodes for ventricular pacing, atrial pacing, atrioventricular sequential pacing and recording intra-atrial and intraventricular electrograms. Such catheters are considered invaluable aids in treating critically ill patients, such as those with complications following acute myocardial infarctions, as well as to monitor cardiac and pulmonary status and maintain fluid balance in patients in shock, congestive heart failure and various other critical conditions.
In the typical arrangement, a multi-lumen catheter is positioned with a lumen opening at the distal end thereof within the right ventricle or pulmonary artery and a second lumen opening in the right atrium. These lumens are then appropriately externally interconnected with pressure-responsive apparatus to monitor pulmonary artery pressure and central venous pressure, respectively.
Since the pulmonary artery pressure is generally the more critical pressure and is sufficiently high to require the use of complex monitoring apparatus such as electro-mechanical or electronic pressure transducers to accurately continuously monitor and record, the output port of the distal lumen is generally connected to a transducer and recording apparatus. The central venous pressure is, of course, somewhat lower. Accordingly, it is common practice to connect the output port of the atrial lumen to a simple water manometer rather than a second transducer, primarily because of cost and equipment availability considerations. While this arrangement is quite cost-effective and generally acceptable, it suffers many disadvantages. For example, transducer-recorded pressures are generally recorded and/or displayed in standard units of millimeters of mercury while the units displayed on a water monometer indicate millimeters of water. Thus attending personnel are required to make a mathematical conversion to record both pressures in equivalent standard units. While the mathematical conversion is quite simple, it is obviously subject to inadvertent human error. More importantly, reading the level of a liquid miniscus is subject to error and obviously quite subjective. Furthermore, accuracy of measurement is dependent upon location of the base reference point with respect to the patient. This not only requires a highly subjective decision on the part of the operator, but may vary widely from operator to operator and with physical movement of the patient. Thus, for these and other reasons, pressure measurement taken using a monometer are generally not reliable as precision measurements.
While it is apparent that a transducer could be used to measure pressures in both output ports, simple economics and equipment availability usually prohibit the use of dual transducers and recording apparatus on one patient.